Adobe Photoshop CS2 CLASSROOM IN A BOOK [Electronic resources] نسخه متنی

Printing

When you're ready to print your image, use the following guidelines for best results:

Print a color composite, often called a color comp. A color composite is a single print that combines the red, green, and blue channels of an RGB image (or the cyan, magenta, yellow, and black channels of a CMYK image). This indicates what the final printed image will look like.

Set the parameters for the halftone screen.

Print separations to make sure the image separates correctly.

Print to film or plate.

Printing halftone separations

To specify the halftone screen when you print an image, you use the Screen option in the Print with Preview dialog box. The results of using a halftone screen appear only in the printed copy; you cannot see the halftone screen onscreen.

When you print color separations, you print four grayscale screens, one for each process color. Each screen contains halftone information for the respective channel, including screen frequency, screen angle, and dot shape.

The screen frequency controls the density of dots on the screen. Since the dots are arranged in lines on the screen, the common measurement for screen frequency is lines per inch (lpi). The higher the screen frequency, the finer the image produced (depending on the line-screen capability of the printer). Magazines, for example, tend to use fine screens of 133 lpi and higher, because they are usually printed on coated paper and on high-quality presses. Newspapers, which are usually printed on lower-quality paper, tend to use lower screen frequencies, such as 85 lpi.

The screen angle used to create halftones of grayscale images is generally 45 degrees. For best results with color separations, select the Auto option in the Halftone Screens dialog box (which is accessible through the Print dialog box, as you'll see in a minute). You can also specify an angle for each of the color screens. Setting the screens at different angles ensures that the dots placed by the four screens blend to look like continuous color and do not produce moiré patterns.

Diamond-shaped dots are the most commonly used in halftone screens. In Photoshop, however, you can also choose round, elliptical, linear, square, and cross-shaped dots.

NoteBy default, an image will use the halftone screen settings of the output device or of the software from which you output the image. You usually don't need to specify halftone screen settings unless you want to override the default settings. And you should always consult your prepress partner before specifying halftone screen options.

In this exercise, you'll adjust the halftone screens for the postcard image, and then print the color separations.